Goniometric multi-axis positioners (generally called “goniometers” and “goniophotometers”) have been available for a number of years in the lighting industry. Goniometers are used to accurately and precisely position and orient a test object at a plurality of positions in order to evaluate the object's photometric properties, for example the spatial luminous intensity distribution of a light emitting or light reflecting object. Goniometers are typically described as having either a “Type A” or “Type B” configuration. An example Type A goniometer 10 is shown in FIG. 1, while a Type B goniometer 100 is shown in FIG. 2.
With reference to FIG. 1, Type A goniometer 10 is a common configuration used in the transportation lighting industry. Goniometer 10 includes a test platform 12 attached to an inner frame member 14 and is rotatable with respect to the inner frame member about an axis of rotation “X1.” Inner frame member 14 is attached to an outer frame member 16 and is rotatable with respect to the outer frame member about an axis of rotation “Y1.” Thus, the “left-right” rotational axis X1 is nested within the tilt or “up-down” axis Y1. This basic configuration is widely used to test automobile, aircraft and other transportation lighting devices.
With reference to FIG. 2, Type B goniometer 100 includes a platform 102 attached to a horizontal member 104. Horizontal member 104 is rotatably attached to a frame member 106. Platform 102, horizontal member 104 and frame member 106 are all rotatable together about an axis of rotation “X2.” Platform 102 and horizontal member 104 are also further rotatable together about a tilt axis “Y2.” As can be seen from FIG. 2, Type B goniometer 100 is configured such that rotational axis X2 is located beneath tilt axis Y2. Accordingly, the entire frame 106 of the goniometer rotates for the right-left motion. This type of goniometer is commonly used for testing of displays and commercial lighting fixtures.
Some variations of the basic goniometer design exist. For example, some goniometer systems have been built in a “half frame” configuration 200, shown generally in FIG. 3. In the half-frame configuration a platform 202 is fixed to an inner frame 204, the inner frame being cantilevered from an outer frame 206. Platform 202 is rotatable about a rotational axis X3. In addition, inner frame 204 and platform 202 are rotatable together about a tilt axis Y3. A test object (not shown for clarity) may also be adjusted to a desired height H3 by fixturing or tooling equipment that is either incorporated into platform 202 or is detachably coupled to the platform.
The open-end cantilever goniometer 200 of FIG. 3 has some advantages over the closed-box frame designs of FIGS. 1 and 2 due to the lack of an outer frame 206 member at an unsupported end 208 of inner frame 204. As can be appreciated by comparing FIG. 3 with FIGS. 1 and 2, an outer frame 206 member proximate end 208 could interfere with the movement of inner frame 204 in situations where a large test object is attached to platform 202. However, given that many vehicle lighting devices have a left-hand and a right-hand configuration, there is still the potential for interference in some testing scenarios. For example, while no test object-to-outer frame 206 interference may be experienced at the unsupported end 208 of inner frame 204, interference between the test object and the outer frame may still occur on the opposing, supported side of the inner frame. The nature of the half-frame goniometer design also requires a relatively large, heavy structure and massive bearing assemblies to minimize positional error with regard to platform 202 due to deflection of the cantilevered inner frame 204. In some cases this drawback lends an advantage to the box closed-frame designs of goniometers 10, 100 due to their inherently balanced weight distribution.
A third configuration of goniometer, known as a “sector gear positioner” 300, is shown in FIG. 4. This positioner is a reapplication of a type of positioner used for antennae and artillery aiming devices. A platform 302 is affixed to a large sector gear 304 and is rotatable about a rotational axis X4. The sector gear 304 is coupled to a gear drive 306 that moves the sector gear and platform together to predetermined positions about a tilt axis Y4 having a range of motion θ4. A test object (not shown for clarity) may also be adjusted to a desired height H4 by fixturing or tooling equipment that is either incorporated into platform 302 or is detachably coupled to the platform.
A disadvantage of sector gear positioner 300 is that the range θ4 of up-down motion of platform 302 is limited to a tilt angle of about ±30 degrees from a horizontal orientation due to the sector gear 304 interfering with a light emission path of a test object mounted to the platform at tilt angle extremes. For most transportation lighting it is necessary to run some tests with the light emission of the test object oriented to about a 90-degree “up” position. This is particularly true with respect to forward lighting, such as headlamps for automobiles, as well as aerospace lighting. The “down” direction, i.e., the light emission of the test object oriented to about 180-degrees from the “up” position, is not as much of an issue because all goniometers are limited in this direction due to the mounting requirements of most test objects.
As can be appreciated from the foregoing discussion, current goniometers suffer from significant limitations with regard to the size and shape of objects that can be tested, due to the potential for interference between the test object and the structure of the goniometer. This interference limits the range of motion of the goniometer, in turn limiting the amount of photometric data that can be gathered. Current goniometers also typically consume a significant amount of laboratory space that could otherwise be used for other purposes. Furthermore, available goniometers are typically extremely heavy, making them expensive to transport and requiring significant foundational support at their point of installation. There is a need for a goniometer that addresses these shortcomings.